Method of vulcanizing rubber



Patented Dec. 15, 1942 METHOD or vuromrzn c. RUBBER Howard I. Cramer, Cuyahoga Falls, Ohio, assignor to M. C. T. Corporation, New York, N. Y., a corporation of New Jersey No Drawing. Application April 11, 1939, Serial No. 267,315

18 Claims.

The present invention relates to the vulcanization of rubber and more particularly to new ac- 1 celerators therefor.

More particularly the present invention relates to the vulcanization of rubber in the presence of metal dithiocarbamates which contain an aromatic radical and an alkyl radical having at least four and not more than five carbon atoms, the preferred compounds being those of the divalent metals as for example lead, zinc, cadmium, mercury, tin and the like. Examples of monovalent dithiocarbamates coming within the scope of the present invention are sodium, potassium, and ammonium compounds containing an aromatic radical and an alkyl radical having at least four and not more than five carbon atoms. Other dithiocarbamates which may be used, in accordance with the present invention are those of selenium and tellurium and of the elements of the B family of the group IV of Mendeleefis Periodic System of th Elements including -arsenic, antimony and bismuth compounds containing an aromatic radical and an alkyl constituent of the character herein set forth. Arsenic, antimony and bismuth comprise the oddjseries of Mendeleeffs Periodic System of the Elements, as set forth in the Text Book of Inorganic. Chemistry, 1926, Second Edition, Parington, page 606, McMillan & Co., Ltd.

Metal dithiocarbamates of the class above set forth may be represented by the following formula N-tLs M where R is an alkylmadical containing not less than four and not more than five carbon atoms and AB. is selected from the group of aromatic or aromatic-like radicals; and M is any metal, as for example, sodium, potassium, zinc, lead, cadmium, tin, mercury, arsenic, antimony, bismuth, selenium, tellurium, or ammonium, the latter for the purposes of the present disclosure functioning as a metal. The letter :1: represents an integer equal to the valence of the metal M. In said formula, the radicals R and AR are identical in all dithiocarbamic acid residues attached to the metal.

It may be pointed out that it has been discovered that the metal dithiocarbamates which contain an aromatic radical or an aromatic-like radical and an alkyl radical having at least four and not more than five carbon atoms have great solubility in rubber, and produce in a relatively short time vulcanized rubber having a high modulus and ultimate tensile strength. While the heavy metal dithiocarbamates of the character above set forth form the preferred accelerators of the present invention, the monovalent, trivalent and tetravalent metal mixed alkyl aromatic. dithiocarbamates containing not less than four and not more than five carbon atoms in the alkyl radical also give satisfactory results.

It has been ascertained that the most advantageous accelerators, as will be pointed out in detail later on, are the butyl and amyl aromatic or aryl dithiocarbamates of the metals, and particularly those metal dithiocarbamates wherein the aryl radical or constituent is a phenyl, naphthyl or anthryl radical, or radicals of that character substituted in any manner, as will be hereinafter set forth.

Moreover, it has been ascertained that the accelerators of the present invention function to augment the activity at the vulcanizing temperature of those accelerators which have been so modified as to decrease the tendency of the accelerators to scorch at processing temperatures, but simultaneously have become somewhat inactive at and adjacent the vulcanizin'g temperature. One of the broad discoveries of the present invention is the ability of the herein described mixed alkyl aryl dithiocarbamates of the metals to augment the activity of any accelerator which has been modified to decrease its scorching action at the elevated curing temperature and simultaneously has had its activity reduced.

It has been discovered that when the metal alicyclic aryl dithiocarbamates are used in a rubber stock in conjunction with a component containing selenium and tellurium, that not only will the resultant vulcanized rubber have a high resistance to abrasion, but the rubber also will have a high resistance to tear.

In this connection it may be pointed out that while the use of a selenium and/ or tellurium component in rubber increases the resistance of the rubber to abrasion, these substances are not effective in increasing the resistance of the rubber to tear. Broadly, this phase of the present invention resides in treating a rubber stock containing a component, selected from the group consisting of lements and compounds of selenium or tellurium, or both selenium and tellurium, said component functioning to increase the resistance to abrasion of the vulcanized rubber, in the presence of an agent functioning with said component to increase both the resistance to abrasion and to tear of the finally vulcanized rubber. It may be pointed out that vulcanization in the presence of a selenium and/or tellurium component speeds up the rate of cure so that under ordinary conditions of processing there results in reality an over-cure, the latter producing a decrease in tear resistance. According to the present invention the rubber is compounded or treated with a. component selected from the group consisting of elements and compounds of selenium and/ or tellurium, said component, while functioning to increase the resistance of the rubber to abrasion, causing over-cure, said rubber material being also treated with an agent retarding the normal decrease in tear'resistance of the vulcanized rubber resultin from the increased cure. This decrease in tear resistance may, in accordance with the present invention, be substantially completely prevented.

It has also been discovered'that if liquid rubber dispersions including the natural occurring latices, artificial latices, synthetic latices, and rubber cements are vulcanized in the presence of the accelerators of the present invention, that no pre-vulcanization occurs at room temperature and there is no gelling or setting up at room temperatures of the latex'or the like.

In this connection, it is desired to point. out that it has been previously proposed to vulcanize latex with the higher-dialkyl dithiocarbamates of the metals, but the accelerators of this class are characterized by their tendency to bring about pre-vulcanization at room temperature resulting in a gelling or setting up of the latex composition. The introduction of an aryl group into a higher dialkyl dithiocarbamate of a metal in place of one of the alkyl groups tends to decrease the rate of cure at room temperatures of rubber vulcanized with the modified alkyl aryl dithiocarbamate, the alkyl radical being of the character herein set forth. Such an accelerator when used to vulcanize latex substantially prevents pre-vulcanization at low temperatures, that is, around room temperature, and simultaneously functions to give at higher temperatures a vulcanizate having excellent physical properties. The use as an accelerator of latex of said alkyl aryl metal dithiocarbamates avoids air curing of liquid rubber dispersions exemplified by latex compositions. Stated differently, at low curing temperatures such as emplayed in vulcanizing latex, it is not possible to adequately vulcanize with the lower alkyl, aryl metal dithiocarbamates, while with those dithiocarbamates containing an alkyl radical having more than three carbon atoms and particularly those containing the butyl and amyl groups, vulcanized rubber is obtained having excellent physical properties.

In practicing the present invention, the alkyl radical may be any radical having more than three carbon atoms, the preferred alkyl radical being of the parafiinic type and having the general formula:

. used, as for example, benzyl, beta-phenyl-ethyl and the like. The furalkyl radical may be alpha furfuryl', alpha tetra-hydro-furfuryl or alpha furyl-propyl.

The alicyclic group may be any alicyclic group as for example a* ring compound of which hexyl,

cyclohexyl is representative, said compound being typical of constituents of a group having the general formula:

Oman-1- Other examples of this type are methyl cyclohexyl or hexahydro-tolyl, hexahydro-xylyl and the poly-alkyl substituted cyclohexyls.

The alicylic group may also be hydrindyl, C9H9-, ac-di-hydronaphthyl, C10H9, ac-tetrahydronaphthyl, CmHu, ac-hexahydronaphthyl, C1oH13-, decahydronaphthyl, C1oH11, alpha or beta, or alkyl substituted hydro-naphthyl groups such as ethyl-ac-tetrahydronaphthyl,

alpha or beta, hydroacenaphthyl, hydroanthryl (from hydrogenated anthracene) and hydrophenanthryl (from hydrogenated phenanthrene) or hydroxenyl (from hydrogenated diphenyl).

In the above formula AR defines any aryl group such as phenyl C6H5- or substituted phenyl groups as for example tolyl, CHaCsHaxylyl (CH3)2C6H3, ortho, meta or para cumyl, (CH3) 2CHC6H4 or naphthyl, C10H7- or substituted naphthyl, alpha or beta such as ethyl naphthyl, C2H5CioH6. It is desired to point out that the aryl group may comprise a condensed aromatic ring and in that connection the naphthyl compounds above set forth are illustrative of aromatic rings of this character which may be used in carrying out the present invention. Other examples of aryl radicals containing condensed aromatic rings are indyl, CsH7, acenaphthyl, C12Hv, fluoryl, C13H9-, anthryl C14H9, or phenanthryl C14H9 The aryl. radical may also be those derived TABLE I Parts by weight Pale crepe Zinc oxide '5 Sulphur 2.5 Stearic acid 1 Accelerators in variable amounts as will be hereinafter indicated.

The following table sets forth accelerators which may be used in carrying out .the present invention.

TABLE II M. P Dithlocarbamate Appearance in degiees C.

Zinc normal-butyl phenyi. Cadmium butyl phenyl. Lead butyl phenyl Zinc mixed-arnyl phenyl do- Cadmium primary-amyl phenyl Yellow cryst Cadmium secondary-amyl phen o Cadmium nuxed-amyl phenyl .do Lead primary-amyl phenyl Bufl' powder- 109ll Lead secondaryamyl phenyl d 63-5 Lead nnxed-amyl phenyl Vise. liquid.-- Zinc ac-tetrahydro-beta-naphthyl phenyL. Grey resin.. 64-6 Oadmiuin ac-tetrahydro-beta -naphthyl p eny Buff powder 294-5 Lead ac-tetrahydto-beta-naphthyl phenyl. .do M840 These metal dithiocarbamates including the addition salt were all prepared in accordance with the disclosure of U. S. Patent No. 2,258,847, granted Oct. 14, 1941, to Howard I.,Cramer.

In the above table, reference is made to zinc, cadmium and lead mixed amyl phenyl dithio- Further tests were made with a number of dithiocarbamates as set forth in Table V, using the following compound:

carbamates. These compounds were prepared TABLE Iv by the reaction in an ethyl alcohol solution of Parts by weight a mixture of someric amyl amhnes, carbon disulfide and the weak acid salts of the respective Pale crepe 10 metals, said isomeric anilines being composed Zin OYdP essentially of a mixture of primary amyl and Sulphur 2.75 secondary amyl anilines. A

ccelerator 1.0

The following table sets forth the results obtained by vulcanizing at 260 F. (127 C.) pale crepe compounded as set forth in Table I with certain of the specified dithiocarbamates. The results obtained by vulcanizing the com- TABLE III Parts of Ultimate Max.

Time to Modulus Dithiocarbamatc fiifg g opt. curc gfgg g at 700% ag fiz rubber 1bs./sq. in. cent Zinc n.-propyl phenyl. 0.5 2985 2460 750 Zinc n.-butyl phcnyL. 0.55 21) 3590 1920 765 Cadmium n.-butyl phenyl 0. 50 15 3975 2120 810 Lead n. buty] phenyl..." 0. 68 20 4470 690 Zinc secondary amyl phen 0. 45 3060 1350 800 Cadmium primary amyl phen 0. 60 10 4130 2740 775 Zinc tetrahydro-betanaphthyl phenyl 0. 5 30 3030 1200 835 tensile strength thereby indicating that this class of dithiocarbamates are ultra accelerators as this term is used in the art. In other 'words, while this class of dithiocarbamates are exceed- I ingly fast, there is also coupled therewith the desirable physical properties which it is always desirable to confer upon the finally vulcanized rubber. Not only are the. accelerators exceedingly fast, but they are whatmay be termed non-fugitive accelerators. It is well known in the art that while certain accelerators are exceedingly fast, they are fugitive," that is, they do not maintain the vulcanization reaction at elevated curing temperatures commonly used in factory operations.

Referring to Table III, it is to be noted that when rubber was vulcanized with .6 of 1% of cadmium primary amyl phenyl dithiocarbamate, the rubber attained its optimum cure in 10 minutes and the physical properties of the rubber were exceedingly good. Not only was the optimum cure reached in 10 minutes but vulcanization had progressed very far in 5 minutes. The cadmium n.-butyl phenyl dithiocarbamate when added to rubber in the ratio specified, caused an optimum cure in 15 minutes with remarkably good physical properties.

Not only were tests made of the accelerators set forth in Table III, but all of the accelerators set forth in Table II were tested in the compound of Table I or its equivalent, the temperature of vulcanization being 260 F. Excellent results were obtained for'each of the specified accelerators.

pound of Table IV at 214 F. (101 C.) are as follows:

Referring to Table V, it is to be noted that when using zinc methyl phenyl dithiocarbamate, even after 75 minutes of cure, the stock had not reached its maximum physical properties as indicated by the low ultimate tensile strength of 2275 pounds per square inch. The zinc ethyl phenyl dithiocarbamate acts somewhat better than the zinc methyl phenyl dithiocarbamate, inasmuch as in 45 minutes the vulcanized rubber had reached its optimum cure. The mixed alkyl aryl metal dithiocarbamates having more than three carbon atoms in the alkyl radical produce vulcanized rubber having excellent physical properties and have other advantages which are obvious from the data presented in the table.

The solubility in benzene of the metal alkyl aryl dithiocarbamates, including those having more than three carbon atoms in the alkyl group are setforth in the following table:

TABLE VI Solubility grams per Dithiocarbamntc 100 grams of benzene Zinc methyl phenyl (1. 18 Zinc ethyl phenyl 1.75 Zinc gropyl phenyL. 4. 9 Zinc utyl phenyl 24. 4 Zinc amyl phenyl 17. l Lead butyl phenyl 41. Cadmium butyl phcnyl... 6. 2

Referring to the zinc salt which is illustrative ofv any of the metal salts and particularly heavy metal salts, it is to be noted that zinc propyl phenyl dithiocarbamate is almost three times as soluble in benzene as the zinc ethyl phenyl dithiocarbamate 'and that the zinc butyl methyl phenyl dithiocarbamate is about fourteen times as soluble as the zinc ethyl phenyl dithiocarbamate.

Cadmium alkyl aryl dithiocarbamate having more than three carbon atoms in the alkyl radical has a high solubility in benzene, it being,

' of course, recognized that the solubility in benzene is indicative of the order of the solubility of the metal dithiocarbamate in rubber hydrocarbon.

.It is desired to point out that while the entire class of the higher alkyl aryl dithiocarbamates of the metals give excellent results, themost advantageous and outstanding results are given by the butyl and amyl phenyl dithiocarbamates of the metals and particularly those in which the aryl constituent is a phenyl or naphthyl radical. ,While in the illustrative examples given in Table V, the aryl radical is a phenyl radical, it is within the province of the present invention to substitute for the phenyl radical other aryl radicals as hitherto pointed out, it being again desired to call attention to the fact that the aryl radical or group may comprise a condensed aromatic ring such as the naphthyl group, the anthryl group, the phenanthryl group, the indyl group and aromatic hydrocarbons with two or more benzene nuclei as for example, those derived from diphenyl, terphenyl, the univalent groups from diphenyl being called xenyl. In place of the phenyl radical there may be substituted the aromatic-like radicals such as pyridyl, quinolyl,

fury] and thiophyl.

In the accelerators set forth in Table II and Table V, the alkyl and/or aryl radicals bonded to the nitrogenatom may have introduced therein substituent groups such as a halogen atom, as for example chlorine and bromine, or a halogen-containing group; a nitro group; a nitroso group; a nitrile group; an amino group; an acylamino group; a mercapto group; a sulfonic acid group; a carbonyl-containing group; a carboxy group; an alkoxy group; and/or a hydroxy group. These groups or radicals are merely illustrative of suitable groups which may be introduced into said aryl and/or alkyl group, and this phase of the invention is not limited to said illustrative examples.

The alkyl aryl dithiocarbamates of the metals where the alkyl group contains more than three carbon atoms and particularly where the alkyl group is a butyl or amyl radical, give excellent Zz'nc butyZ-phenyl-dithiocarbamate in results in accelerating the vulcanization of liquid rubber dispersions such at latex compositions.

The following examples illustrate the vulcanization of liquid rubber dispersions and particularly latex compositions with alkyl aryl dithiocarbamates of the metals having an alkyl group with more than three carbon atoms. Accelerators of this type were compounded in a. rubber mix in accordance with the following formulas:

Zinc sec. amyl-phenyl-dithiocarbamate 0.5

The following tables set forth the results of physical tests made upon test slabs poured from the above compositions, the slabs in each case being cured at -93 C.

TABLE IX composi-- tion of Table VII Ultimate Time of cure 3386 tensile 3 23 minutes strength 8 g lbs/sq ll] lbs/sq in per cent 15 l, 620 3, 730 855 l, 700 3, 440. 850 l, 820 4, 250 875 l, 770 3, 840 840 Y 1, 810 3, I60 775 TABLE X Zinc sec. amyl-phenyl-dithiocarbamate in composition of Table VIII Modulus Ultimate Max T of cure ll2)itl800% tensileh elongation minutes s. sq. in. s reng lbs/sq. in. per cent The herein described accelerators may be used for the vulcanization of liquid dispersions of artificial or synthetic latices or rubber. More par,- ticularly, said accelerators may .be used in the vulcanization of raw rubber or reclaimed rubber; rubber cements and synthetic latices typified by those derived from thiohol, that is polyalkylene polysulfides, neoprene and butadiene polymers. Suitable alkyl aryl metal dithiocarbamates are zinc, lead, cadmium, tin, mercury, antimony, arsenic, bismuth, selenium, sodium, potassium, ammonium and the like.

The dispersions of the character herein set forth may be vulcanized in the presence of the amine-addition compounds of the broad class of metal dithiocarbamates and, more particularly, the dithiocarbamates herein-referred to. As an example of such an addition-compound reference is made to the zinc cyclohexyl phenyl dithiocarbamate pyridine addition product having a melting point of 308 to 310 C. A further example is zinc n.-butyl phenyl dithiocarbamate, n.-butyl amine addition product having a melting point of 126 to 127 C. These addition products are representative of the broad class of amine addition products which may be formed with the alkyl aryl dithiocarbamates of the metals where the .alkyl group has three or more carbon atoms or where the alkyl group is an alicyclic radical or cycloalkyl radical. At this point, it may be stated that the alicyclic aryl dithiocarbamates coming within the scope of the present invention may be substituted as is herein pointed out.

The structural formula. for zinc cyclohexyl phenyl dithiocarbamate and cadmium ac.-tetrahydro-beta-naphthyl phenyl dithiocarbamate is as follows:

Zinc cyclohexyl phenyl dithiocarbamate:

Cadmium ac.-tetrahydro-beta-naphthyl phenyl While in these compounds the cyclohexyl radical has been set forth as an illustrative example of a suitable alicyclic radical, it is within the province of the present invention to substitute for this alicyclic radical any other alicyclic radical, as for example, hexahydro-tolyl, hexahydroxylyl and in general, any polyalkyl cyclohexyl radical. The alicyclic group may also be hydrindyl, C9H9; ac.-di-hydronaphthyl, CmHuac.-tetrahydronaphthyl, CioH--; decahydronaphthyl, C1oH17-; alpha or beta, alkyl substituted hydro-naphthyl groups such as ethyl ac.-tetrahydronaphthyl, C2H5- C1oH1o; alpha or beta,

, cyclohexyl phenyl hydroacenaphthyl; hydrofiuoryl; hydronanthryl (from hydrogenated anthracene), hydrophenanthryl (from hydrogenated phenanthrene) or hydroxenyl (from hydrogenated diphenyl). The phenyl group is illustrative of a suitable aromatic group and in lieu of said phenyl group, there may be substituted a tolyl group as for example, tolyl, CH3CsH4-; xylyl (CI-I3)2C6Ha; ortho, meta or para cumyl, (CH3)2CH CsH4; naphthyl, Cl0H7; or alpha or beta substituted naphthyl as for example, ethyl naphthyl, C2H5C10Hs. The aryl group may also comprise a condensed aromatic ring. In that connection the naphthyl groups above referred to are illustrative aromatic rings which may be attached to the same nitrogen atom as the alicyclic radical.

It is within the province of the presen inven tion to substitute in the alicyclic radical or the aryl radical various non-metal substituents, for example, a halogen atom, of which chlorine and bromine are illustrative; a nitro group; a nitroso group; a nitrile group; an amino group; an acylamino group; a mercapto group; a sulfonic acid group; a carbonyl-containing group; acarboxy group; an alkoxy group; and/or a, hydroxy group. While the above are illustrative of suitable substituting substituents, the present invention is not limited thereto.

As illustrative of the physical properties conferred upon vulcanized rubber by the use of the metal alicyclic aryl dithiocarbamates, the data relative to certain tests is set forth. The following examples indicate the results obtained by vulcanizing rubber with the metal alicyclic aryl dithiocarbamates and particularly the metal dithiocarbamates. More particularly, zinc and lead cyclohexyl phenyl dithiocarbamates were used to vulcanize a compound having the following formula:

The results of the physical tests are presented in the following table, taken on specimens cured at 275 F. for varying times, are:

TABLE XII Zinc and lead cyclohexyl dithiocarbamates in a typical tread stock 33 Modulus Maximum Dithiocarbamatc Strength at 500% elongation m lbs/sq. 1n. per cent Zin cyclohexyl phenyl:

3 minutes 1305 690 710 '15 minutes s 3050 1330 760 I 30 minutes 4400 1940 770 45 minutes 4925 2050 710 60 minutes 4000 2000- 700 minutes 3980 2140 600 minutes 3960 2270 G80 Lead cyclohexyl phenyl:

5 minutes 1280 590 675 10 minutes... 2560 990 710 20 minutes. 4285 1740 735 30 minutes... 4665 '2160 700 45 minutes 4330 2110 710 60 minutes 4120 2180 690 For purposes of the following discussion, accelerators may be divided into those that produce during vulcanization what is known as a plateau effect and those which do not. The accelerators of the dithiocarbamic acid series and particularly the metal dithiocarbamates hitherto used do not give, during vulcanization of rubber compounds, the desired plateau effect. However, the metal dithiocarbamates containing both an alicyclic radical and an aryl radical function admirably to produce the desired "plateau effect which is clearly indicated in Table XII. Y

In other words, referring to the data showing results of tests when zinc cyclohexyl phenyl dithiocarbamate is used to vulcanize a typical tire tread stock, it is to be noted that the optimum tensile strength is reached in a relatively short period, namely 30 minutes and that the tensile strength thereafter is held very near the optimum strength for a period of 120 minutes. If the tensile strength is plotted as the ordinate and the time of cure is plotted as the abscissa, the resulting curve is one that goes up rather quickly at the beginning and then maintains itself as an approximate straight line or only slightly departing from its maximum level, the latter part of the curve illustrating the plateau effect. As stated, most of the metal dithiocarbamates hitherto used do not give the plateau effect. The introduction of the alicyclic radical in combination with the aryl radical into a metal com pound of the dithiocarbamates and particularly the heavy metals, although not limited thereto, does give the desired plateau effect. This is of particular value in vulcanizing tire treads or similar thick article where it is necessary to avoid over-vulcanization of the surface layer more or less directly exposed to the vulcanization heat while allowing the more remote portions of the article to be adequately vulcanized.

It may be pointed out that in general, the

metal dithiocarbamates heretofore used do not confer good aging properties upon rubber stocks in which they have been used as accelerators. However, the accelerators of the present invention not only produce vulcanizates which have excellent aging properties, but also produce vulcanizates whose time tensile curves exhibit the plateau effect.

The alicyclic aryl compounds of the metal dithiocarbamates, and particularly the cyclohexyl compounds, function to augment the activity at the vulcanizing temperature of those accelerators which have been so modified as to decrease their tendency to scorch at processing temperatures, but which simultaneously have become somewhat inactive at and adjacent to the vulcanizing temperature. One well known class of accelerators which have been so chemically modified to decrease their scorching tendency is the mercaptothiazole class of which dibenzothiazyl disulfide is an outstanding example, this compound being known as Altax. This compound is illustrative of delayed action accelerators which may be regarded as chemical derivatives of known powerful accelerators in whichthe active hydrogen atom has been replaced by less active organic groupings which during vulcanization -are capable of undergoing decomposition, hydrolysis, fission, or other reaction to reform a very active accelerator combination. More specifically, Altax is representative of the dithio-ether class of accelerators. Another example of this class is 2-(2,4-dinitro-phenylthio) -benzothiazole. Another group of delayed action accelerators which may be activated by the cycloalkyl aryl dithiocarbamates are. the thio-esters which are exemplified by Z-benzothiazole thio-benzoate. Another representative class comprises the thioanhydrides, as for example, tetramethyl thiuram disulfide and tetra cyclopentamethylene thiuram monosulfide. A further representative class is the substituted amino benzothiazyl sulfides, exemplified by the following:

CeHu

\ Cellu The cycloalkyl aryl metal dithiocarbamates, and particularly those of the heavy metals, function to activate accelerators of the character above referred to, and particularly Altax at elevated curing temperatures typified by a curing range of about 260 to 275 F. In other words, the alicyclic aryl metal compounds, whether unsaturated or having substituents of the character previously referred to introduced therein, function to augment the tensile strength and modulus which is produced by the herein set forth chemically modified accelerators.

It may be stated that the alicylic aryl dithiocarbamates of the metals of which the cyclohexyl aryl dithiocarbamates are typical examples, are chemically inert at low vulcanizing temperatures towards a great many accelerators, as for example Altax, and therefore accelerators of the character herein set forth may be used to augment the activity of any primary accelerator to which it is substantially chemically inert at low vulcanizing temperatures, that is, temperatures below 260 to 275 F., the point being that broadly the accelerators of the present invention may be used to augment the activity of any accelerator adapted to cure at a high temperature, as for example, 260 to 275 F., provided the two accelerators are mutually inert at temperatures below the above vulcanizing range. In other words, the above accelerators may'be designated 1 ticed elevated curing temperatures. a

as delayed action activator accelerators since the accelerators of the present invention do not begin to assist in the vulcanization of the rubber stock until the stock approaches the vulcanization temperature, that is, when the temperature begins to rise to'or adjacent the normally prac- In the present disclosure, while reference has been made to the use of cyclohexyl aryl dithiocarbamate of the metals, it is to be'understood that instead of using the cyclohexyl dithiocarbamate of the metals, other cyclo-alkyl aryl dithiocarbamates of the metals and particularly heavy metals, may be used as accelerators, as for example, the cyclopropyl, cyclobutyl, cyclopentyl, cycloheptyl and cyclooctyl aryl dithiocarbamates of the metals.

Referring to Table XI, it is to be noted that the metal alicylic aryl dithiocarbamate is used as an accelerator in conjunction with sulphur. However, in accordance with the present invention, a new result is obtained if the metal alicyclic aryl dithiocarbamates are used as accelerators in conjunction with amix containing selenium and/or tellurium elements or compounds or selenium and/or tellurium elements or compounds in conjunction with sulphur. The selenium or tellurium constituent is preferably used in therubber mix in the form of a solid solution of selenium and sulphur, although it may be present either in a finely divided form or in a dispersed form. Further, all or a portion of the Selenium and/or tellurium may act as a vulcanizcomprising a primary accelerator ing agent. When the metal alicyclic aryl dithiocarbamates, exemplified by a metal cyclohexyl phenyl ,dithiocarbamate, as for example, zinc, is used to vulcanize rubber, the resultant rubber is not only excellently vulcanized, but has a high resistance to abrasion and a high resistance to tear even in rubber which has been cured for extended periods of time at the normal curing temperature of about 260 to 275 F.

In general, it may be stated that as the time of cure increases, the resistance to abrasion also increases, but simultaneously, the tear resistance of the vulcanized rubber decreases. It has been discovered that when the metal alicyclic aryl dithiocarbamates, the latter being typified by cyclohexyl phenyl dithiocarbamates of zinc are used in a mix containing a selenium and/or tellurium constituent, that there is a retardation of the decrease in tear resistance which normally results from the increased state of cure induced by the presence of the selenium and/or tellurium constituent. This is a significant advance in the art. There is no doublt that the use in a rubber mix of selenium and tellurium constituents in any of the forms above set forth and particularly when the selenium and/or tellurium is in a solid solution, greatly increases the resistance to abrasion of the vulcanized rubber, but, utilizing the present invention there is a retardation in the decrease in tear resistance which normally results from the over-cure. The present invention efl'ectively solves theproblem presented.

It is desired to pointout in this connection,

that the cycloalkyl radical may be a cyclopropyl,

cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl or higher alkyl radicals, and these alkyl radicals may have substituents introduced therein as hereinbefore clearly pointed out. The aryl radical is preferably, although not necessarily, a phenyl radical, although in lieutthereof other aryl radicals may be present in thealicyclic aryl metal dithiocarbamates, as hereinbefore pointed out.

In the follomng table, there is set forth a rubber compound containing Altax, the latter typifying a chemically modified accelerator which needs activating to attain its greatest accelerator action, the activator being zinc cyclohexyl phenyl dithiocarbamate. The rubber compound also contains a solid solution of sulphur and selenium.

TABLE XIII Parts by weight Smoked sheets 100 Carbon" black. 45 Zinc oxide Stearic acid ,4 Pinetar 3 Phenyl beta naphthyl amine 1 Dibenzothiazyl disulfide 0.5

Zinc cyclohexyl phenyl dithiocarbamate 0.05 Sulphur-selenium solid solution 80 S:

20 Se 2.22 Sulphur 2.0 Selenium 0.22

cause the vulcanized rubber to have a high resistance to tearing. Experiments show that good tear resistance with the other qualities above set forth is not obtained if the metal alicyclic aryl dithiocarbamates is omitted from the rubber compound. As stated, other cyclo-alkyl aryl dithiocarbamates of the metals and particularly the heavy metals may be substituted in place of the zinc cyclohexyl phenyl dithiocarbamate.

Table XIV sets forth results of tests made on the rubber vulcanized in accordance with the mix set forth in Table XII.

TABLE XIV Zinc cycloheacyl phenyl dithiocarbamate in composition of Table XIII cured at 275 F.

Q3 Modulus Maximum Time of cure Strength at 500% elongation lbslsq'jm lbs./sq. in. per cent I 15 minutes 1350 040 710 30min11tes..,.. 3410 2060 670 minutes 4305 2860 650 minutes 5160 3840 625 minutes 7., ,.l 5165 4150 570 minutes 4540 4060 520 It is obvious that the accelerator herein set forth may be mixed with other accelerators or anti-oxidants commonly well known in the art.

It is within the province of the present invention to vulcanize with selenium and/or tellurium mixed alkyl aryl dithiocarbamates of the character herein set forth. The alkyl radical which may be a saturated or unsaturated radical, may

have substituentsintroduced therein, as previous- 1y pointed out. The aryl or aromatic, or aromatic-like radical may be any of the radicals and these aromatic radicals may have substituents introduced there in of a character similar to thesubstituents the alkyl radicals of the dithiocarbamates.

The compoundset forthin Table XIII illus- I trates the combination of a composite accelerator 7 high resistance to abrasion, such accelerator in no way deleteriously effecting the high resistance of the rubber to abrasion while functioning to such as which have beenstated may be introduced into In this connection, it may be stated that in the entire disclosure of the present invention wherever the aryl or aromatic or aromatic-like radical has been mentioned, it is to be understood that these radicals may have substituents introduced therein of the character hereinbefore referred to when considering the introduction of substituents into the alkyl radicals.

It has been pointed out that not only may the 0 heavy metal compounds of the various dithiocarbamates herein referred to be used as rubber accelerators, but that in lieu of the heavy metals, other metals may be used including arsenic, antimony, bismuth, selenium and tellurium, the dithiocarbamates of any of said metals containing an alkyl radical of the character described and an aryl radical.

The general formula for the mixed aryl alkyl dithiocarbamates of the trivalent metals is as follows:

In the above formula R and AR represent the same entities as herein previously set forth and M represents a trivalent metal typified by arsenic, antimony and bismuth.

, Very satisfactory results have been obtained by vulcanizing rubber compounds and liquid dispersions of the character herein previously set forth with the following metalloid mixed aryl alkyl dithiocarbamates.

Satisfactory results may be obtained by vulcanizing rubber compounds in the presence of a mixture of arsenic and antimony dithiocarbamates or in the presence of a mixture of arsenic, antimony, and bismuth dithiocarbamates. Antimony dithiocarbamate may be mixed with bismuth dithiocarbamate and used as an accelerator. In any of the above mixtures the dithiocarbamate may be, but not necessarily so, a mixed aryl dithiocarbamate.

In accordance with the present invention any of the rubber compositions herein disclosed may be vulcanized in the presence of a dithiocarbamate of the elements arsenic, antimony and bismuth of the B family of group V of Men deleeifs Periodic System of Elements, including the alkyl dithiocarbamates and the aryl dithiocarbamates irrespective of the number of carbon atoms in the alkyl or aromatic group.

The structural formula for selenium and tellurium compounds is as follows:

TABLE XVI Dithiocarbamate Appearance v cent1grade Selenium n-butyl phenyl Orange crystals.-. 120422 Selenium primary amyl phenyL. At room temperatulre viscous red o1 Selenium cyloliexyl phenyl Yellow crystals" 192-194 In general, it may, be stated that the selenium mixed alkyl aryl dithiocarbamates are ultra accelerators.

In the above compounds, the selenium may be substituted wholly or partially by tellurium. The selenium mixed alkyl aryl dithiocarbamates, including the alicyclic aryl-dithiocarbamates typified by the alicyclic phenyl dithiocarbamates of selenium and/or tellurium may be used in a rubber mix in which the vulcanizing agent is sulphur, selenium or tellurium or in a'vulcanizing mix containing a selenium entity such as a solid solution of sulphur and selenium which confers upon the rubber a high resistance to abrasion. Further, in any of the above mixes, part of the selenium and/or tellurium present in the selenium mixed alkyl aryl dithiocarbamates may function at least partially as a vulcanizing agent. It may be pointed out further that these compounds are quite soluble in rubber and accordingly provide an effective means of incorporating soluble selenium into rubber stocks.

For the purposes of the present invention selenium and tellurium may be considered as metals and further, while arsenic and antimony are usually classified as metalloids, it is to be understood that they function analogously to the mono, di, tri and tetravalent metals and therefore, wherever in the present specification and claims, a metal is referred to, it is understood to include the equivalent metalloids, such as arsenic and antimony. I

The term "rubber as used in the specification and claims is limited to a sulfur-vulcanizable rubber and includes synthetic rubber derived, as for example, from butadiene, isoprene, dimethylbutadiene, or other homologues or analogues of butadiene, as well as the ordinary forms of rubber such as latex, balata, reclaimed rubber, gutta percha and the ordinary coagulated forms derived from the Hevea Braziliensis tree or mixtures of such materials.

What is claimed is:

1. The method of vulcanizing a sulfur-vulcanizable rubber comprising vulcanizing it in the presence of a metal dithiocarbamate having the following formula:

AR being the same in all dithiocarbamic acid radicals attached to the metal.

2. Vulcanized rubber comprising the vulcanized reaction product of a sulfur-vulcanizable rubber and a dithiocarbamate having the following formula:

( NCS M AR/ 2:

where R is an alkyl radical containing not less than four and not more than five carbon atoms, AR is an aryl radical, M is a metal, and a: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarba'mic acid radicals attached to the metal.

3. The method set forth in claim 1 in which the alkyl radical is a butyl radical.

4. The method set forth in claim 1 wherein the alkylradical is a butyl radical and the aryl radical is a phenyl radical.

5. The method set forth in claim 1 wherein the alkyl radical is an amyl radical.

6. The method set forth in claim 1 wherein the alkyl radical is an amyl radical and the aryl radical is a phenyl radical.

7. The method comprising vulcanizing a sulfur-vulcanizable liquid rubber dispersion in the presence of a metal dithiocarbamate having the following formula:

where R is an alkyl radical containing not less than four and not more than five carbon atoms, AR is an aryl radical, M is a metal, and a: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal. 1

8. The method comprising vulcanizinz sulfurvulcanizable rubber latex in the presence of a metal dithiocarbamate having the following formula:

NCS M AR 1 where R is an alkyl radical containing not less than four and not more than five carbon atoms, AR is an aryl radical, M is a metal, and :1: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal.

9. The method as set forth in claim 8 in which the alkyl radical is a butyl radical.

10. The method as set forth in claim 8 in which the alkyl radical is a butyl radical and the aryl radical is a phenyl radical.

11. The method as set forth in claim 8 wherein the alkyl radical is an amyl radical.

12. The method as set forth in claim 8 in which the alkyl radical is an amyl radical and the aryl radical is a phenyl radical.

13. The method set forth in claim 1 wherein the metal is a divalent metal.

14. The method of vulcanizing a sulfur-vulcanizable rubber comprising vulcanizing it in the presence of a metal dithiocarbamate having the following formula:

R\ S AR x where R is an alkyl radical containing not less than four and not more than five carbon atoms,

- AR is an aryl radical, M is a metal of the odd series where R is an alkyl radical containing not less than four and not more than five carbon atoms, AR is an aryl radical, M is a metal of group VI of Mendeleefls Periodic System of the Elements, said metal having vulcanizing properties and an atomic weight between 79.2 and 127.5, and a: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal.

16. Vulcanized rubber comprising the vulcanized reaction product of a sulfur-vulcanizable rubber and a dithiocarbamate having the following formula:

where R is a butyl radical, AR is an aryl radical, M is a metal, and x is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal.

17. Vulcanized rubber comprising the vulcan-.

ized reaction product of a sulfur-vulcanizable rubber and a dithiocarbamate having the following formula:

where R is an amyl radical, AR is an aryl radical, M is a metal, and .1: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal.

18. Vulcanized rubber latex comprising the vulcanized reaction product of a sulfur-vulcanizable rubber latex and a metal dithiocarbamate having the following formula:

where R is an alkyl radical containing not less than four and not more than five carbon atoms, AR is an aryl radical, M is a metal, and a: is an integer equal to the valence of the metal, R and AR being the same in all dithiocarbamic acid radicals attached to the metal.

HOWARD I. CRAMER. 

